This invention relates generally to furnaces and, more particularly, to control method and apparatus for responding to overtemperature conditions in a furnace.
In downflow furnaces, the circulating air blower and its drive motor are located above the heat exchanger, whereas, in horizontal furnace, the blower and drive motor are located to one side of the heat exchanger. In either the downflow or the horizontal furnace, if a blower motor fails to operate properly in its normal manner while the burner is on during the heating cycle, the temperatures within and around the furnace will tend to rise. It is therefore desirable that such a condition be sensed and that the resulting temperatures not be allowed to reach excessive levels. In downflow furnaces, especially, the filters are located above the blower compartment which in turn, is located above the heat exchangers; and when the blower motor fails, the heat rises by natural confection causing an overtemperature condition in the blower compartment so as to thereby expose the filter to excessive temperatures.
One approach to addressing this problem is to provide, along with a temperature sensing device, a switch that opens in response to such overtemperature conditions. The switch can then be manually reset when the sensed overtemperature condition has been corrected. However, with such a manual switch, there will be occurrences of nuisance trips, such as when, for example, a short power interruption occurs just before the blower is to come on. Also in attic installation, where the temperature in the summer exceeds the trip temperature setting, the switch will be tripped open and, subsequently, when cool weather occurs and a call for heat is not responded to, a service call is required to reset the switch.
A preferred approach was therefore to use an automatic reset limit switch which automatically recloses after it cools down. However, it was found that after a certain number of consecutive overtemperature cycles resulting from a blower motor failure, the maximum allowable temperature of the material used in the air filters was exceeded.
It is possible to provide a single furnace design which can be used either in the upright (i.e., a downflow configuration) or a horizontal disposition. While it is desirable to have a single type of overtemperature control to respond to the overtemperature conditions as discussed hereinabove, it was recognized that the sensitivity to such overtemperature conditions would be different for a given furnace, depending on whether it is in the upright or in the horizontal position. For example, since it is desirable to sense the temperature within the furnace blower compartment, and since the heat from the heat exchanger tends to rise thereabove, a sensor would be exposed to higher temperatures when the furnace is in an upright position than when it is in a horizontal position such that the sensor is at one side rather than above the heat exchangers. It therefore becomes more complicated to have a single design of an overtemperature system that will accommodate either position of installation.
It is therefore an object of the present invention to provide an improved control system for overtemperature conditions.
Another object of the present invention is the provision in a gas furnace having overtemperature control, for avoiding nuisance trips which then require manual resetting before proper operation resumes.
Yet another object of the present invention is the provision for an overtemperature control system in a furnace which can be operated in either the upright or the horizontal positions.
Still another object of the present invention is the provision in a gas furnace for an overtemperature control system which is economical to manufacture and efficient and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.